The present invention relates to an ink ribbon for a thermal transfer printer. More particularly, the invention relates to an ink ribbon for a thermal transfer printer comprising a foundation and a thermal transfer layer provided on the foundation, portions of which layer are selectively softened or melted to be transferred to a receiving medium by selectively controlling the heat generation of a plurality of heating elements provided on a heating head.
The ink ribbon of such a type generally used heretofore includes one wherein a thermal transfer colored ink layer containing a wax-like substance as a main component of the vehicle of the ink is provided on a film-like foundation. The ink ribbon provides clear images on a smooth paper. However, there is the problem that clear images cannot be obtained on a rough paper because the ink does not reach the concave portions of the rough paper, which results in formation of transferred ink images with poor edge definition or voids.
An attempt was made wherein a thermoplastic resin having a film-forming property was incorporated into the colored ink layer in addition to the wax-like substance to improve the film-forming property of the ink layer, and the ink layer was transferred on a rough paper so that the transferred ink layer spanned the concave portion of the rough paper where the ink did not reach like a bridge, as schematically shown in FIG. 1. In FIG. 1, reference numerals 1, 1a and 1b indicate a rough paper, the convex portion of the paper an the concave portion of the paper, respectively. Reference numeral 2 indicates the colored ink layer transferred. The transferred ink layer 2 is adhered to the paper at the convex portions 1a but the ink layer 2 is out of contact with the paper at the concave portion 1b and spans the concave portion 1b like a bridge.
By means of the above technique wherein the ink layer is transferred so that it spans the concave portions of the receiving medium like a bridge, the transferred ink image is free of poor edge definition and voids, and clear images can be obtained on a rough paper similarly in the case of transfer on a smooth receiving surface.
According to the above-mentioned technique utilizing the ink bridging, it was made possible to print not only on a smooth receiving paper as in the conventional method but also on such a rough paper as mentioned above by means of a thermal transfer printer, which resulted in a further enhancement of utility of the thermal transfer printer.
In such a situation, a printer capable of printing at a high speed of about 100 cps (corresponding to a head moving velocity of about 260 mm/sec) or more was recently put to practical use.
In the case of such a high-speed printer, it was impossible to produce clear images on a rough paper even by using the ink ribbon utilizing the ink bridging and the usable receiving paper was restricted to a smooth paper.
On the other hand, in the case of thermal transfer printers, the distance (hereinafter referred to as "peeling distance") between the position where some portion of the ink ribbon is heated wit the heating head and the position where said heated portion of the ink ribbon is peeled off form the receiving paper (both positions are relative ones with respect to the heating head) or the period of time (hereinafter referred to as "peeling time") between the time when some portion of the ink ribbon is heated with the heating head and the time when said heated portion is peeled off form the receiving paper (herein after, the peeling distance and the peeling time are generically referred to as "peeling condition") varies depending upon kinds of machines. Under the circumstances, there were some cases where an ink ribbon, which was able to provide clear images in a printer with a peeling condition, was not able to provide clear images or absolutely any image in another printed with a different peeling condition.
It is an object of the present invention to provide an ink ribbon for thermal transfer printer capable of providing clear images not only n a smooth paper but also on a rough paper even in a high-speed printing or even on printers with different peeling conditions.
This and other objects will become apparent from the description hereinafter.